1. Field of the Invention
The present invention relates generally to the field of treatment of spent etchant yielded from the manufacturing process of milling printed circuit boards. More particularly, the present invention relates to the field of recovery of copper and regeneration of ammoniacal etchant from spent ammoniacal etchant yielded from milling printed circuit boards in electronic and computer industries.
2. Description of the Prior Art
Printed circuit boards are widely used in many electronic and computer devices. A chemical milling process is commonly utilized in manufacturing printed circuit boards. In a typical chemical milling process, an etchant contained in an etchant solution etches the copper (Cu) plated or covered printed circuit board. One of the most commonly employed etchants in the electronic and computer industries is ammoniacal etchant which contains ammonia (NH.sub.3) and ammonium chloride (NH.sub.4 Cl).
At the end of the milling process the etchant solution eventually becomes saturated with copper (Cu) and thus unusable. The unusable etchant solution yielded from the milling process is known in the industry as "spent etchant". If an ammoniacal etchant is used, it yields what is known in the industry as "spent ammoniacal etchant".
It has become a substantial environmental problem to dispose of spent etchant without any treatment after the milling process. The reason is that the spent etchant contains a significant amount of copper (Cu) and disposal of copper (Cu) is rigorously restricted under environmental laws and regulations.
In addition, disposing of spent etchant without any treatment results in great economic loss. In the case of disposal of spent ammoniacal etchant, not only significant amounts of copper (Cu), but also of ammonia (NH.sub.3) and ammonium chloride (NH.sub.4 Cl) are lost.
There have been two basic approaches to recovering copper (Cu) from the spent etchant. One basic approach is to recover copper (Cu) through an electrolytic process. The other basic approach is to recover copper (Cu) through a chemical reaction process. The electrolytic process is generally not commercially available because it has not yet been proven practical.
U.S. Pat. No. 4,252,621 issued to Reinhardt et al. on Feb. 24, 1981 for "Process of Regenerating An Ammoniacal Etching Solution" (hereafter the "Reinhardt Patent") has disclosed a "LIX" system utilizing a chemical reaction process for the treatment of spent etchant and the recovery of copper (Cu) from the spent etchant. The "LIX" system disclosed in the Reinhardt Patent utilizes an organic agent to separate copper (Cu) from the spent etchant and then converts the separated copper (Cu) into copper sulfate (CuSO.sub.4). The major disadvantage of the Reinhardt Patent is that both the capital and the operation costs of the LIX system are very high, which has substantially limited its commercial application.
There is therefore an urgent need for an effective and economic process of treating the spent etchant yielded from the milling of printed circuit boards in electronic and computer manufacturing industries. Particularly, it will be desirable to having a method and apparatus which is able to not only recover copper (Cu) contained in spent ammoniacal etchant but also regenerate the ammoniacal etchant from the spent ammoniacal etchant, where the regenerated ammoniacal etchant can be used again in the milling process.